The HIV epidemic is rapidly unfolding in Vietnam. The growing group of HIV-infected infants and children has limited access to diagnostic testing and preventive clinical interventions. In this setting where minimal pediatric HIV research infrastructure exists, a study of the epidemiology of pediatric HIV infection in Vietnam and evaluations of early diagnostic testing and monitoring algorithms would establish the necessary baseline data from which to develop subsequent research interventions. The overall objective of this application is to support the principal investigator's development into an independent clinical researcher in pediatric HIV epidemiology. To accomplish this objective, the proposed program has both training and scientific components. The training component of this application includes completion of a Master of Public Health degree program that will provide formal training in study design, epidemiologic methods, and biostatistics, with a focus on international health and policy issues. A diverse group of mentors will facilitate clinical and research experiences that will guide career development. The scientific component of this application tests the hypothesis that the "ultrasensitive" heat-dissociated signal-amplified p24 antigen assay is a sensitive and specific alternative to standard DNA PCR for diagnosing HIV in pednatally-exposed infants in Vietnam. In addition, alternative ("second tier") surrogate laboratory markers - including total lymphocyte count, p24 antigen levels, hematocrit/hemoglobin, and albumin - will be compared to CD4 and RNA viral load, under the hypothesis that these more easily accessible markers are similady associated with clinical disease progression in HIV-infected infants. These hypotheses will be tested in the context of a prospective cohort study of perinatally-exposed infants in Ho Chi Minh City. Infants will have regularly scheduled clinical evaluations and quality-controlled laboratory testing for diagnosis and monitoring. The principal investigator will spend extended research time in Ho Chi Minh City to conduct the study. Descriptive, univariate, and multivariate analyses will be performed to compare laboratory results and clinical outcomes. The findings of this study may result in more widespread access to HIV diagnostic testing in Vietnam, and the development of feasible laboratory monitoring algorithms for future pediatric care and treatment programs.